DNA Adsorption And Desorption Characteristic Of Variable And Constant Charge Soils And Minerals

The characteristics of adsorption and desorption of DNA by variable charge soils and colloids (red siol and latosol), permanent charge soils and colloids (chao soil and cinnamon siol), minerals (goethite, montmorillonite and kaolinite) and Layered double hydroxide were studied using the batch and the soil column leaching methods. The main results were drawn as follows:1.In monovalent electrolytic system (NaCl and KCl), the decreases of DNA adsorption on the Red siol and the Latosol and the Chao soil and the Cinnamon soil colloids were observed with the increase of DNA solution pH. The maximum amounts of adsorbed DNA on the soil colloids were kept about 13.1~14.8μg/mg in solution pH from 2.0 to 4.0. It was largely droped with solution pH from 4.0 to 8.0 that the decrease ranges of the permanent charge soil colloids may reach 85.7. There was a remarked difference when adsorbed DNA was desorbed by NaOAc and NaH2PO4 solution in the variable charge soil colloids and the permanent charge soil colloids. The desorption percentages were 10%~24.5% in the former and 72.3%~85.9% in the later when desorbed by NaOAc solution, and it was 23.5%~40.2% in the former and 8.8%~21.6% in the later when desorbed by NaH2PO4 solution. It indicated that DNA was adsorbed mainly by ligand exchange on the variable electric charge soil colloids when mainly by electro-static force on the permanent charge soil colloids. In Goethite surfaces, the amount of adsorbed DNA was 14.88~15.56μg/mg, and increased with solution pH from 2.0 to 3.3, and was constant when solution pH values were more 3.3. As for Montmorillonite and Kaolinite, the amounts of DNA adsorption decreased with increasing the solution pH from 2.0 to 8.0. The former droped from 15.30 ~15.75μg/mg to 4.13~2.44μg/mg and the latter from 13.82~14.45μg/mg to 3.14~2.44μg/mg. when the solution pH was form 2.0 to 8.0.2.In the divalent electrolytic system (MgCl2 and CaCl2), the amounts of adsorbed DNA in variable charge and permanent charge soil colloids were different when the solution pH increased. The amounts of adsorbed DNA in the former were kept about 13.0~15.0μg/mg. It increased at first and then dropped in the latter, and the max amount was 14.39~15.22μg/mg when solution pH was 4.5. The amounts of DNA adsorbed followed the order of Goethite> Montmorillonite> Kaolinite. The amounts of adsorbed DNA were little change with the variation of the solution pH in Goethite and Montmorillonite. The maximum amounts were 14.66~14.77μg/mg in Kaolinite when the solution pH values were 2.0~3.5, and then dropped to 7.72~9.14μg/mg when the solution pH values were 3.5~8.0.3.The adsorption isotherm data of soil colloids, minerals and layered double hydroxides were obtained using the batch method. Langmuir and fruendlich equation could fit DNA adsorption very well and the determination coefficients (r2) were more 0.90. The amount of DNA adsorbed followed the order of the permanent charge soil colloids>variable charge soil colloids. The affinity of DNA adsorption followed the order of Kaolinite > Montmorillonite > Goethite. In the experiment of layered double hydroxides, the determination coefficients (r2) were more 0.92 when fitted by Langmuir equation, and the affinity followed the order of nano-Al(OH)3> nano-MgAl2> nano-Mg2Al> nano-Mg(OH) 2.4.The permanent charge soils were disposed of calcium-carbonate. It was found that the amount of adsorbed DNA of de-calcium-carbonate soils more than that of calcium-carbonate. The desorbed percentages in de-calcium-carbonate Chao soil and Cinnamon soil were much more than that in calcium-carbonate Chao soil and Cinnamon soil when desorbed by NaOAc solution, and the desorption percentages were similar when desorbed by NaH2PO4 solution. It indicated that there were electro-static force which was the mainly interaction between CaCO3 and DNA.5.The influence on adsorbed DNA containing the heavy metal of Cu ion and Cd ion solutions was that Cu ion may provide more adsorption sites than Cd ion when DNA concentrations were low, and Cd ion may provide more adsorption sites than Cu ion when DNA concentrations were high in the red soil colloid, and the amounts of adsorption sites provided by Cu and Cd ions were similar when DNA concentrations were low, and Cd ion may provide more adsorption sites than Cu ion when DNA concentrations were high in the Latosol colloid.